In a process for producing a semiconductor device, it is necessary, for example, to remove a native or natural oxide film (e.g., SiO2) formed on a wafer at the bottom of a contact hole of a semiconductor substrate (semiconductor wafer). As a technology for removing the natural oxide film, various proposals have been made for the technology using hydrogen in the radical state (H*) and NF3 gas (see, for example, Patent Document 1).
With the technology disclosed in Patent Document 1, a processing gas is introduced into a processing chamber rendered in a predetermined vacuum state to react the processing gas with an oxidized surface of a silicon wafer (SiO2) disposed in an atmosphere in the predetermined vacuum state, thereby forming a reaction product (NH4)2SiF6. Then, the processing chamber is heated to control the silicon substrate to a predetermined temperature. As a result, the (NH4)2SiF6 is sublimated to remove the natural oxide film on the surface of the silicon substrate (etching).
In recent years, there has been a growing demand for the degree of cleanliness of the surface of the silicon wafer (single crystal silicon, polysilicon) deprived of the natural oxide film. Along this line, further purity has been demanded for the silicon surface after removal of the natural oxide film. On the silicon surface as an interface with the natural oxide film, oxygen may be present in interstitial spaces of the silicon. Even after removal of the natural oxide film, it is likely for oxygen to remain.